Forced convective boiling heat transfer of water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm inner-diameter circular tube has been investigated for both horizontal and vertical upward flows. Boiling heat transfer rates of the test fluids were determined experimentally over a range of mass flux, vapor mass quality, and inlet subcooling through a boiling data reduction procedure that allowed analytical calculation of the fluid boiling temperatures along the experimental test section by applying ideal mixture and equilibrium assumptions along with Raoult’s law. Based on the experimental findings that the heat flux in the nucleation-dominant-boiling region was dependent strongly on the wall superheat but almost independent of the mass flux and the inlet subcooling, prediction equations were developed for boiling heat transfer coefficients of water and ethylene glycol/water mixtures in small channels. The equations predict the experimental data well, and most of the predicted values are within ±30 % of the experimental data.